Usually when this happens to me, I close Dropbox (quit the application), wait a ...

ninjastar99 on Nov 28, 2010 | parent | context | favorite | on: Why does Dropbox download so slowly?

Usually when this happens to me, I close Dropbox (quit the application), wait a few minutes, then re-open it. Typically that fixes the slow speed and ramps it back up to capacity (I'm on Verizon Fios).